Protected magnetic core element



June 13, 1961 M PIZZA 2,988,674

PROTECTED MAGNETIC CORE ELEMENT Filed May l, 1958 Figi INVENTOR. mmzzA BY y n/,10K

AT TORNE Y United States Patent O M 2 988 674 PROTECTED MAGNEirIc CORE ELEMENT Michael Pizza, Maynard, Mass., assignor to Minneapolis- Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Filed May 1, 1958, Ser. No. 732,209 9 Claims. (Cl. 317-458) A general object of the present invention is to provide a new and improved magnetic core element for use in electrical circuits. More specifically, the invention is concerned with a new and improved magnetic core element formed of a wound magnetic metal tape wherein said core element is protectively surrounded by a covering which is characterized by its ease of manufacture and assembly and its ability to withstand the annealing temperatures to which the core is subjected in the course of its preparation.

Magnetic core elements exhibiting a rectangular hysteresis characteristic have found wide use in certain types of electrical circuits for many purposes such as the performing of logic and the storage of digital information. Certain types of magnetic metals are particularly adapted to respond to physical treatment and thereby produce certain electrical characteristics which enhance the rectangular shape of the hysteresis characteristics of the core material. One way in which these materials are processed is to wind a thin metal tape on a suitable bobbin and then subject the same to an annealing temperature which may be in the vicinity of l000 centigrade. The use of the high annealing temperature has placed a physical limitation on the type of material which may be selected as bobbin material for the tape for the reason that the bobbin must maintain its physical shape during the annealing process.

After the tape wound core on its bobbin has been appropritaely annealed, the end product is normally incorporated in an electrical circuit and in the process has a number of windings passed through the core. In the course of handling the cores during the winding operation and eletctrical assembly, it has been found that any physical stress placed upon the magnetic portion of the core tends to cause a shifting of the electrical characteristics thereof. ln most instances, the shifting of the electrical characteristics may render the core useless in many of its intended places of application. Consequently, there has been a need for a more complete protective covering capable of withstanding the annealing temperatures so that once the core material has `achieved its proper electrical characteristics, it can not be further subjected to physical stress to cause any change in the electrical characteristics thereof.

Ceramic type bobbins have heretofore been used. The use of such bobbins is not desirable for a number of reasons, being the bobbin is fragile and it is difficult to mainatain close tolerances on the dimensions thereof. Further, the use of ceramic as a bobbin material tends to score the insulation from wire being threaded through the bobbin due to the abrasive effect of the ceramic. While coating or painting the bobbin after annealing can be effected, the cost of such additional processing is considable with respect to the over-all cost of the completed unit and in most instances can not be tolerated. Consequently, the use of a material such as a non-magnetic metal which is capable of being machined renders the end product considerably more attractive from the ultimate use standpoint and also from the over-all cost standpoint.

In a copending application of David Shansky and Francis Alla, entitled Electro-Mechanical Apparatus, filed on even date herewith, there is disclosed a tape wound magnetic core which is adapted to have a non- 2,988,674 Patented June 13, 1961 magnetic protective covering surrounding the core with this covering being seletcted to withstand the annealing temperatures required wtih respect tothe magnetic core material used in the apparatus. As discussed in the aforementioned application, one of the elements particularly adapted for use in such a combination is stainless steel so long as it is selected to be a non-magnetic type of steel.

inasmuch as the use volume of magnetic core elements is relatively high, it is essential that any protective covering utilized be relatively inexpensive to manufacture and assemble. As taught by the present invention, a highly suitable bobbin and protective member for the magnetic core is arranged so that the bobbin and the protective member may be locked together by means of a pair of tapered surfaces. Thus, the bobbin member may be formed with a taper on at least one wall portion whereof. A protective sleeve is then made to t over the bobbin and incorporate a matching taper so that when the sleeve is placed on the bobbin, they may be forced into engagement and thereby locked into position. Once assembled with the magnetic tape wound on the bobbin and the sleeve in place, the apparatus is then ready for annealing.

It is, therefore, a more specific object of the present invention to provide a new and improved magnetic core element having a mounting bobbin and protective sleeve therefor adapted to protectively surround the core land where the sleeve and the bobbin are locked in position by way of a mechanical taper.

In another embodiment of the invention, a bobbin member is provided on Iwhich a metallic magnetic tape is wound. The end walls of the `bobbin are also both tapered and a pair of protective cylindrical sleeves are adapted to fit over the end walls of the bobbin and be locked in position by way of the tapered surfaces.

It is therefore a still further more specific object of the invention to provide a new and improved magnetic core element having a magnetic metal tape wound on a bobbin member whose end walls are adapted to be tapered so as to receive a pair of cylindrical protective sleeves and be locked into engagement `by way of tapered surfaces in the sleeves which co-operate with the tapers on the end walls of the bobbin.

The foregoing objects and features of novelty which characterize the invention, as well as other objects of the invention, are pointed out with particularity in the claims annexed to and forming a part of the present specication. For a better understanding of the invention, its advantages and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

Of the drawings:

FIGURE l is va cross-sectional showing of a preferred embodiment of the invention; and

FIGURE 2 is a cross-sectional view of a modified form of the present invention incorporating a pair of tapered surfaces.

Referring first to FIGURE l, the numeral 10 represents a bobbin member having a first end wall section 12 and a second end wall se'ction 14. Wound upon the bobbin 10 between the end wall portions 12 and 14 is a suitable metallic tape 16 of a magnetic type. The end wall 14 is adapted to have a tapered surface at 18. The taper on this surface is preferably selected to be approximately 1/2 per foot length. Surrounding the tape 16 and adapted to engage the end wall 14 is a protective cylindrical sleeve 20. The inner surface of the sleeve 20 is adapted to have a taper at least at the portion which would engage the taper 1S on the wall 14.

In the course of assembly, the metallic tape 16 is wound on the bobbin 10 with the desired number of of turns. Once the desired number of turns of the tape are in position, the protective sleeve 20 is then forced over the bobbin and the matching taper surfaces engage to provide a mechanical bond. Once assembled, the unit may -be placed in a suitable annealing oven where it may be subjected to an annealing temperature of approximately lO centigrade.

It will be noted that the protective sleeve 2t) does not extend into a point of engagement with the end wall l2. The spacing between the sleeve 2li and the wall l2 is to prevent the forming of an electrical short circuit around the core material 16 to thereby render it useless in an electrical circuit.

The bobbin material is preferably selected to be metal. The metal selected must be capable of withstanding the high annealing temperature of 1000 centigrade. One such metal which is useful is stainless steel having a type number 303. The magnetic tape which is wound upon the bobbin i0 may be selected from that group of ferrous alloys which exhibit rectangular hysteresis characteriscs once having been appropriately treated. One such material which has heen widely used is a molybdenum permalloy formed of 4% molybdenum, 79% nickel, and 17% iron. The `dimensions of a tape which has been used in such a device are 1A thickness with a width of 1/s. The dimensions of the assembled unit with the protective sleeve in place may be, for example, -an outside diameter of approximately 1A, an inside diameter of 1/s, and an over-all length of approximately 1A. It will be apparent that the dimensions selected are directly related to the size and type of magnetic tape which is to be used in the assembled product.

FIGURE 2 represents a modified form of the present invention incorporating the same basic principles. In this instance, there is provided a bobbin 22 having a pair of end walls 24 and 26. Mounted upon the bobbin 22 is a suitable magnetic metal tape.

The end wall portions 24 and 26 are both tapered on the peripheral wall surfaces thereof and the taper may Well be selected to be z per `foot length. Instead of a single protective sleeve, as shown in FIGURE l, the apparatus of FIGURE 2 incorporates a pair of protective sleeves 30 and 32. Each of the protective sleeves has an inner tapered surface which is adapted to match the tapered surface on the periphery of the associated wall section of the bobbin 22. Once these protective sleeves 30 and 32 have been forced into position so that the tapered surfaces are locking, the apparatus may then be placed in a suitable annealing furnace and processed in preparation for subsequent use in an electrical circuit. It will be noted that the sleeve members 30 and 32 do not engage when they are in position on the bobbin 22. The reason they must not engage is that the sleeve and bobbin could form a short circuited turn on the 'core 2S and thereby render the same useless.

While, in accordance with the provisions of the statutes, there has been illustrated and described the best forms of the invention known, it will be apparent to those skilled in the art that changes may be made in the apparatus described without departing from the spirit of the invention as set forth in the appended claims and that in some cases, certain features of the invention may be used to advantage without `a corresponding use of other features.

Having now described the invention, what is claimed as new and novel and for which it is desired to secure by Letters Patent is:

1. A protective apparatus for a magnetic core comprising a nonmagnetic metal bobbin having an end Wall with a peripheral taper thereon, said bobbin being adapted to carry a magnetic metal tape wound on said bobbin, and la covering sleeve of nonmagnetic metal fastened to said bobbin at one end only, said sleeve having an inner taper which is adapted to lock on said peripheral taper and surround on all sides a tape wound on said bobbin.

2. A protective apparatus for a magnetic core as set forth in claim l wherein said metal bobbin and sleeve are formed of stainless steel.

3. A protective apparatus for a magnetic core as set forth in claim l wherein said metal bobbin and sleeve are formed of a metal capable of withstanding the annealing temperature of said magnetic tape.

4. In combination, a bobbin, said bobbin comprising a center -cylindrical portion and a pair of cylindrical end wall portions, at least one of said wall portions having a taper on the peripheral surface thereof, said bobbin being adapted to have a magnetic tape wound thereon, and a protective sleeve formed over the center cylindrical portion of said *bobbin and engaging said bobbin at one end only, said sleeve comprising a hollow cylindrical member having an inner surface, at least a portion of which is tapered to lock with the taper on said one wall portion.

5. In combination, a nonmagnetic metal bobbin, said bobbin comprising a center cylindrical portion and a pair of 'cylindrical end wall portions, at least one of said Wall portions having a taper on the peripheral surface thereof, said bobbin ybeing adapted to have a magnetic tape Wound thereon, and a protective sleeve of nonmagnetic metal formed over said tape and engaging said bobbin at one end only, said sleeve comprising a hollow cylindrical member having an inner surface, at least a portion of which is tapered to lock with the taper on said one wall portion.

6. In combination a stainless steel bobbin, said bobbin comprising a center cylindrical portion and a pair of 'cylindrical end wall portions, at least one of said wall portions having a taper on the peripheral surface thereof, a magnetic tape wound on said bobbin, and a protective stainless steel sleeve formed over said tape and engaging said bobbin at one end only, said sleeve comprising a hollow cylindrical member having an inner surface, at least a portion of which is tapered to lock with the taper on said one wall portion.

7. In combination, a bobbin, said bobbin having a central cylindrical section and a pair of end wall sections, said end wall sections each having a taper on the peripheral surface thereof, said bobbin being adapted to have a magnetic tape wound thereon, and a pair o'r hollow sleeves having tapered inner surfaces, said sleeves being locked onto the tapers of said Wall sections to project over said bobbin without engaging each other.

8. In combination, a nonmagnetic metal bobbin, said bobbin having a central cylindrical section and a pair of end wall sections, said end wall sections each having a taper on the peripheral surface thereof, said bobbin being adapted to have a magnetic tape wound thereon, and la pair of hollow nonmagnetic metal sleeves having tapered inner surfaces, said sleeves being locked onto the tapers of said wall sections and extending over said bobbin Without engaging each other.

9. In combination, a stainless steel bobbin, said bobbin having a central cylindrical section and -a pair of end wall sections, said end wall sections each having a taper on the peripheral surface lthereof, a magnetic tape wound on said Ibobbin, and a pair of hollow stainless steel sleeves having tapered inner surfaces, said sleeves being locked onto the tapers of said wall sections and extending over said bobbin without engaging each other.

References Cited in the file of this patent Performance-Guaranteed Tape Wound Cores, Catalog TWC-A; Magnetics Incorporation, March 1955, particularly pages 21-23, 27 and 28. 

